Q. Find the value of the following expression and round to the nearest integer:n=2∑2240(1.2)n−1Answer:
Recognize as geometric series: Recognize the sum as a geometric series. The general form of a geometric series is ∑n=0∞arn, where a is the first term and r is the common ratio. In this case, a=40(1.2)2−1=40(1.2) and r=1.2.
Calculate first term: Calculate the first term of the series.The first term is when n=2, so we have a=40(1.2)2−1=40(1.2)=48.
Use formula for sum: Use the formula for the sum of a finite geometric series.The sum of the first k terms of a geometric series is given by Sk=(1−r)a(1−rk), where k is the number of terms. Here, k=22−2+1=21 terms.
Calculate sum: Calculate the sum of the series.Using the formula from Step 3, we have S21=48(1−1.221)/(1−1.2).
Perform calculations: Perform the calculations.S21=1−1.248(1−1.221)=−0.248(1−1.221)=−240(1−1.221).
Calculate exact value: Calculate the exact value of 1.221. 1.221 is approximately 109.41898913151242 (using a calculator).
Substitute value into sum: Substitute the value from Step 6 into the sum.S21=−240(1−109.41898913151242)=−240(−108.41898913151242)=26020.55747150297.
Round to nearest integer: Round the result to the nearest integer.The sum rounded to the nearest integer is approximately 26021.
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